The present invention relates generally to an optical apparatus and, more particularly, to an optical scan-type tunnel microscope applying an energy transfer phenomenon.
Conventionally, a structure of an optical scan-type tunnel microscope shown in FIG. 2 is described for example in "The Optics" vol. 20, No. 3, pp. 134-141. The microscope includes an optical fiber 8 having a core portion 3 and a clad portion 4. The end surface of the clad portion 4 is covered by a light shielding film 5. At an end of the core portion 3, there is a head portion which is smaller in size than a wavelength of light. The microscope further comprises a Z-axis transfer mechanism 11 and a control mechanism 12 for causing the surface of a sample 2 to be measured to fully approach and to be positioned at the head portion of the optical fiber, and an XY-axis transfer mechanism 9 and a control mechanism 10 for causing the head portion of the optical fiber to scan the surface of the sample 2. The microscope further comprises a prism 1 for leading in light so that the light totally reflects on the surface of the sample, a light source 13 and an optical system 14 for generating the illuminating light, and a light detecting system 15 for measuring light which is a part of evanescent light generated on the outside of the surface of the sample under the aforementioned condition of total reflection and which passes to the other end of the optical fiber by infiltrating through the optical fiber from the head portion thereof.
As it is apparent from the aforementioned document, the optical scan-type tunnel microscope is able to measure a structure such as an irregularity on the surface of a sample in a resolution that exceeds by far a resolution of about a wavelength in optical microscopes which are restricted by the limitation of the diffraction of light, by utilizing the evanescent light whose amplitude attenuates exponentially and by an optical probe having a fine opening within a distance of about a wavelength in a normal direction on the surface of the sample.
However, the resolution of the optical scan-type tunnel microscope has been low as compared to that of a scan-type tunnel microscope because the exponential attenuation of the amplitude of the evanescent light along with the increase of distance from the sample surface is slow as compared to an attenuation of a tunnel current flowing between a fine conductive needle and a sample in the scan-type tunnel microscope, and because the sensitivity for detecting light is lowered due to the reduction in diameter of the aperture which significantly lowers the possibility for the evanescent light to infiltrate into the optical fiber.
On the other hand, although a sample of the scan-type tunnel microscope needs to be conductive, a sample of the optical scan-type tunnel microscope just needs to be transparent and needs not be conductive. As the optical scan,type tunnel microscope has such a merit, there has been a demand to enhance its resolution by any means.